Electric cables



Oct. 15, 1957 B 2,810,011

ELECTRIC CABLES Filed Dec. 18, 1950 5 Sheets -Sheet 1 Inventor HARVEYBUM? Attorney Oct. 15, 1957 H. BURR 2,810,011

ELECTRIC CABLES Filed Dec. 18, 1950 3 Sheets-Sheet 2 26 26 {I I l I (a)27 (6) I l" Inventor 3/ -HRVE Y BUER Attorney Oct. 15, 1957 Y H. BURR2,810,011

ELECTRIC CABLES Filed Dec. 18, 1950 s Sheets-Sheet 3 3/ f X L 26 27 26Attorney illnite tates Patent ELECTRIC CABLES Harvey Burr, London,England, assignor to International Standard Electric Corporation, N ewYork, N. Y., a corporation of Delaware Application December 18, 1950,Serial No. 201,348

Claims priority, application Great Britain December 23, 1949 6 Claims.(Cl. 174-117) This invention relates to the manufacture of electriccables and has particular reference to multi-conductor telephone cables.

The basic unit of one form of conventional telephone cable is usuallythe twisted pair of paper insulated conductors. Such twisted pairs areusually made by first applying a helical lapping of paper tape to eachwire and then twisting the insulated wires together. This processinvolves two separate operations and moreover the speed is limited bythe fact that there is a limit to the speed at which the paperinsulation can be applied without breaking. Careful handling isnecessary to avoid stripping off the insulation.

Numerous attempts have been made to avoid applying the paper as ahelical lapping but they have not been found completely satisfactory.

It is also known to insulate a pair of wires simultaneously by passingthe wires and an insulating tape through a bath of molten insulatingcompound while the tape is being folded around the wires. This wrappingholds the wires in position as it passes into a cooling bath where theinsulating compound solidifies. This is essentially a very low speedprocess, slower than the conventional method of lapping a tape helicallyaround each wire individually. Moreover the thickness of insulationaround the wires is considerable and the presence of the insulatingcompound renders the wire unsuitable for use in telephone cable.

There is also known a process of applying an insulating strip in theform of an 8 about a pair of conductors leaving air space between eachconductor and surrounding strip. in this type of process the insulatingstrip is necessarily made of stiff insulating material because thematerial retains its 3-fold without requiring heat or adhesives to fixthe fold. This type of insulation about a pair of wires isunsatisfactory because the wires are unsupported in the surrounding airspace and the electrical characteristics of the pair varies to such anextent along the length of the pair that a cable made up of a pluralityof such pairs would be completely unsatisfactory for telephone purposes.in addition, each pair occupies a greater space than a pair in thenormal type of cable and thus, the construction would lead to anincrease in cable diameter which is costly, as well as, space consuming.

An object of the present invention is to provide means by which twowires forming a pair can be simultaneously insulated to form a compactpair useful in multi-conductor telephone type cable. Another object isto provide such means which enables the two wires to be simultaneouslyinsulated and to be twisted immediately thereafter.

According to a feature of the present invention the two wires to formthe pair are passed through a die through which there is also passed astrip of insulating material wide enough to provide at least one turnround each wire, the die being so shaped that the wires are graduallybrought closer together and the said strip is rolled around the twowires. The invention will be 2,810,01 I Patented Oct. 15, 1957understood from the following description taken in conjunction with theaccompanying drawings from which it will be appreciated that theinvention comprises an improved process and apparatus for insulatingelectrical conductors particularly for the manufacture of communicationcables.

In the drawings:

Fig. l is a purely diagrammatic representation of the apparatus forcarrying out the process according to the invention,

Fig. 2 illustrates diagrammatically a portion of one form of insulatedpair cable according to the invention,

Fig. 3 represents a detail of the apparatus,

Fig. 4 represents in simplified form the insulating die for carrying outthe process,

Fig. 5 represents in perspective a practical form of die,

Fig. 6 shows in greater detail one construction of die,

Fig. 7 shows in detail another construction of die.

In Fig. 1 conductor wires 1, 2 are supplied from reels not shown andpassed around two pulleys 3, 4 which are braked by means of frictionbelts 5, 6 the tension of which is controlled by weights 7, 8. The twowires then pass through a guide member 9 through which there are twochannels guiding the wires so that they will approach the insulating die10 at the correct angle. The strip of paper 11 is supplied from a reel,not shown, and passes directly into the guide member 9 which ensuresthat it is fed into the insulating die 10 correctly.

The only function of guide member 9 is to assemble the paper strip andthe wires correctly for feeding into the insulating die. In Fig. 3 thereis shown a cross section of the guide member 9 which will be referred tolater.

Fig. 2 shows on an enlarged scale a portion of an insulated pair ofwires produced by the process. The two wires 1 and 2 are insulated by anS-shaped wrapping of paper 12 of which one side carries distinguishingmarks as shown. It can be seen that the wires are insulated from oneanother and that the inner edges of the insulating paper are held downby the outer turn of paper .so that the two wires are completelycovered.

\eturning now to Fig. 1. After the two wires and the strip of paper havepassed through the guide member 9 they pass to the insulating die 10which will be de scribed in more detail below. In this die the paper isWrapped round the two wires in the 5 formation shown in Fig. 2. It is tobe mentioned that if desired more turns can be wrapped around the wiresthan the one and a half turns shown in Fig. 2.

The die 10 is heated as is conventionally indicated in Fig. l by aBunsen burner 13. As explained earlier this heating facilitates thepassage of the paper through the die. The paper, which is somewhathygroscopic, is passed in an undried condition and therefore containsconsiderable moisture. It is believed that the evaporation of themoisture from the pores of the paper results in the production of avapour cushion which enables the paper to be drawn through a well shapeddie at high speed. In practice the temperature of the die is fairlyaccurately controlled according to the conditions obtaining by means ofa thermostat, but a temperature of 220 C. represents an average valuewhich has been found satisfactory. The presence of the water vapour alsoproduces an ironing effect so that the coating of insulation is smoothand retains its shape. After the insulated pair emerges from the die 10it passes round the draw oif capstan 14 which is suitably mounted on asupport 15 and driven by a motor, not shown. It can be seen that thetension on the wires between the pulleys 3, 4 and the capstan 14 isdetermined by the friction exerted by the belts 5, 6 and can thereforebe controlled by the correct selection of the weights 7, 8.

This tension is important as it is desirable to apply the insulationwhile the wire is slightly extended so that after the insulated pairleaves the capstan 14 the wires will contract slightly with the resultthat the paper insulation will not be under tension. This provides amargin so that the paper will not be so taut that it is liable to breakif the insulated pair is bent or stretched during the subsequentoperations involved in twisting and laying the insulated pairs up intocable form. After the insulated pair leaves the capstan 14 it passesround a tensioning device before being wound onto the take up drum 17.The object of the tensioning device is simply to ensure that there isenough tension on the pair to cause the pair to wind correctly on thedrum. It is important that the tension on the pair after it leaves thecapstan should be less than that on the pair before it reaches thecapstan as explained above. The form of tensioning device 16 shown issuitable because it does not allow the tension to increase suddenlyowing to any irregularities in the rotation of the take up drum 17.

Itis usually desirable to twist the pair before it is laid up into acable both for electrical reasons such as the reduction of cross talkand also to eliminate any tendency for the wires to roll against andunwind the insulation. For this purpose the take up drum 17 is mountedin a twisting yoke 18 which can be rotated about an axis coinciding withthe line of approach of the insulated pair.

The twisting yoke 18 is geared to the drive of the capstan 14 and thegearing can be set to provide the precise twist length required.

Referring to Fig. 3 the guide member 9 consists of two metal blocks 19,20 provided with grooves 21, 22 through which the wires 1, 2 (seeFig. 1) pass. These grooves 21, 22 which are also indicated in Fig. 1,lead the wires along approaching paths while a strip of paper 11 passesthrough a rectangular channel 23 formed by the shaping of the metalblocks 19 and 20. The channel 23 is in practice only a narrow slitaccommodating a strip of thin insulating paper 11 but it has been shownon a rather exaggerated scale to make the arrangements clear. The slitis however appreciably wider than the thickness of the paper to allowfor irregularities. The blocks 19, 20 are held together by screws 24,25. After the wires and paper have passed through the guide member 9they next enter the insulating die 10 where the process of wrapping thepaper longitudinally about the wires takes place.

Fig. 4 illustrates diagrammatically the principle of the insulating die.In Fig. 4(a) there is shown the intake end of the die there being twoapertures 26 connected by a narrow slit 27. At the output end of the dieshown in Fig. 4(b) the two apertures 26 are so close together that theslit has virtually vanished. Fig. 4(c) is a plan view of the die showingthe two channels 26 converging. The diameter of the channels 26 isgradually slightly increased as they come closer together since a littlemore space is required as the paper is wrapped round the wires.

In Fig. there is shown an exploded view of a practical form ofinsulating die. The two parts shown under (a) and (b) are identical inshape. Considering (b) first, this is formed of two blocks 28, 29mounted on top of one another and fixed rigidly together. Fig. 4(a)shows the co-operating part, which is identical in shape with that shownin (b) but placed the other way up, and is formed of two blocks 3!), 31rigidly fixed together. The blocks 28 and 29 have arcuate grooves 32 and33 cut along their appropriate edges while blocks 30 and 31 have grooves34 and 35 out along their appropriate edges.

It is to be noted that none of the blocks 28, 29, 3t), 31 have thegeneral form of rectangular parallelepipeds. Block 28 is wider at itsdistant end (as shown) than at its near end, and this is also true ofblock 31. Blocks 29 and 30 are wider at their near ends than at theirdistant ends. When these two parts, Fig. 5(a) and (b) are broughttogether the grooves 32 and 33 form with grooves 34 and 35 respectivelythe channels 26 shown in Fig. 4 and the slit 27 is the space betweensurface 36 of block 29 and the under surface 37 of block 30 which,surfaces it will be seen have been slightly cut away at 38 and 39 fromthe general level of the mating surfaces of the blocks 28, 29 and 3t),31 respectively. When the two parts of the die shown in Fig. 5(a) and(b) are brought together the actual die passage will be as shown in Fig.4 and the external shape of the die will be, as drawn, a rectangularparallelepiped. The outer shape of the die is however of no importancein connection with the invention.

There are inevitably some irregularities in the paper and at times itwill be necessary to make a join in the paper as for example when asupply reel is exhausted. It is necessary therefore to arrange theblocks forming the die in such a way that they can separate slightly toallow a thickened portion of the paper to pass, and such an adjustmenthas to be rather delicate since the paper is fragile.

In Fig. 6 there is shown in more detail a die constructed with thegeneral design described immediately above and illustrated in Fig. 5.

Blocks 28 and 29 are shown mounted on a base plate 40 and rigidly fixedtogether and to the base plate by a screw 41. Blocks 30 and 31 arerigidly fixed together by screw 42, but are slidable on the base plate.A spring 43 acting between a stop member 44 and the top of the unitformed of blocks 30 and 31 keep the unit pressed against the base plate.Another spring 45 acting between a stop member 46 and the side of theunit formed of blocks 30 and 31 keep the unit pressed up against theunit formed of blocks 28 and 29. The stop members 44 and 46 are madeadjustable so that the pressure exerted by the springs can becontrolled.

It can be seen that if a place where the paper strip is thicker or widerthan usual passes into the slit 27 the unit formed of blocks 30 and 31can move upwards or sideways and the paper will not be damaged. Theentrance to the die may be slightly bell mouthed to enable the oversizepaper to enter and cause the unit to move.

The die need not however be built up of four blocks and in Fig. 7 thereis shown a die formed of an upper block 47 mounted on a lower block 48.The passage through the die so formed may be of the same shape andproportions as that in the four block die of Figs. 5 and 6. It ishowever still desirable to allow for variation in the paper width andthickness and this necessitates designing the assembly so that the upperblock 47 can move slightly with respect to the lower block 48 and thisinvolves a somewhat different structure from that shown in Fig. 6.

In Fig. 7 the lower block 48 is rigidly fixed to a baseplate 49 whichforms part of a rigid framework 50 by means of screws 51. The upperblock 47 is slidably mounted on the block 48 as shown. It is held inposition by a system of rods which allow it a limited freedom ofmovement.

Thus rods 52 are rigidly held in the framework by engagement with thebase plate and the upper member of the frame 5%) by the nuts 53.

Where the rods pass through block 47 however they are slightly smallerthan the drillings through which they pass. Thus the upper block is onlypermitted a limited movement in the right and left direction as shown inthe drawing. Similarly one or more rods 54- pass through one or moredrillings in the block 47 which have a diameter slightly larger thanthat of rod 54. The rods are held firmly in position in the framework 50by nuts 55. These rods 54 serve to limit the movement of block 37 in theup and down direction.

The upper block t? is pressed down onto block 48 by means of spring 56which is compressed between a plate 57 and the upper surface of block47. The pressure can be controlled by means of hand screw 58. Block 47is also pressed to the left as shown in the drawing by means of spring59 which is compressed between plate 60 and the side of block 47.

The pressure can be controlled by the handscrew 61.

It is to be understood that the particular constructions for the die andits assembly illustrated in Figs. 6 and 7 are only examples andproviding the fundamental shape and proportions of the passage throughthe die are maintained any method of mounting the components which isfound suitable may be adopted.

It will be seen that with the process according to this invention wherethe wires issue from the machine they are close together and half thewidth of the paper strip is wrapped around one wire and the other halfaround the other wire, the edges of the strip being on the inside of thetwo lappings so that there is no tendency for the paper to unwrapitself. The paper strip is so wrapped around the wires that one side isexposed around one wire and the other around the other wire, thewrapping is in fact in the shape of the letter S. This has the advantagethat if paper is printed in colour or otherwise marked on one side it isalways possible to identify the wires of a pair.

It has been found advantageous to heat the die when applying paperinsulation as this greatly facilitates the passage and folding of thestrip and also results in the insulation being as it were baked inposition on the wires. A temperature of 220 C. has been foundsatisfactory.

It can be seen that this process lends itself to the very rapidproduction of twisted pair as there are no high speed rotating parts. Italso has the advantage that a thinner and/or narrower paper can be usedsince there is less danger of breaking. The insulation on the finishedproduct can be more closely packed than with helical lapping and thismeans that a given number of pairs can be accommodated in a smallercable thus saving some of the expensive sheathing material.

If thought desirable a line of perforations can be provided down themiddle of the original paper strip. These would then appear in themembrane between the insulated wires and would facilitate theirseparation for jointing purposes.

Although the invention has been described in connection with paperinsulation it is not limited thereto. Amongst other applications theremay be mentioned the possibility of using textile tapes, or plasticfilms of rubber strip.

While the principles of the invention have been de scribed above inconnection with specific embodiments, and particular modificationsthereof, it is to be clearly understood that this description is madeonly by way of example and not as a limitation on the scope of theinvention.

What I claim is:

1. A process of producing a pair of insulated wires of small overallcross section useful in multiconductor telephone type cable, comprisingpositioning the wires longitudinally of and on opposite sides of a stripof thin insulating paper, wrapping one edge of the strip about one ofsaid wires at least one turn, simultaneously wrapping the other edgeabout the other of said wires at least one turn, and during the wrappingoperation bringing said wires and said insulation together compactly,and applying heat and pressure to iron smooth and permanently set theinsulation around the wires.

2. The process according to claim 1, and further comprising tensioningthe wires during the application of said insulation strip therebyslightly extending said wires, and upon the completion of the processremoving said tensioning from said wires, thereby permitting the wiresto contract in relation to the insulation strip, whereby the insulatedwires may be bent without rupturing the paper.

3. A process of producing a pair of insulated wires of small overallcross section useful in multiconductor telephone type cable comprisingpositioning the wires longitudinally of and on opposite sides of a stripof thin insulating paper, wrapping the opposite edges of said stripabout the respective wires slightly more than one turn, whereby theinner edges of the insulating paper are held down by the outer turns ofpaper so that the two wires are completely covered, and during thewrapping operation bring said wires and said insulation togethercompactly, and applying heat and pressure to iron smooth and permanentlyset the insulation around the wires.

4. A pair of wires, useful in multiconductor telephone type cable,compactly insulated with a thin strip of insulating paper, the strip ofpaper being in the form of an 8, each loop of the 8 extending aroundeach wire respectively approximately one and one-half turns.

5. A pair of wires, useful in multiconductor telephone type cable,compactly insulated with a thin strip of insulating paper, the strip ofpaper being in the form of an 8, each loop of the 8 extending aroundeach wire respectively slightly more than one turn, whereby the inneredges of the insulating paper are held down by the outer turns of paperso that the two wires are completely covered.

6. The product according to claim 3 wherein one side of said strip ofinsulating paper is differently marked from the other whereby themarking on one side of the strip identifies one wire and the marking onthe other side of the strip identifies the other wire.

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